Estimating the elastic modulus of unidirectional over-braided multilayer composites

Abstract

Unidirectional over-braiding was developed based on two-dimensional over-braiding. Unidirectional over-braided multilayer composites have excellent mechanical properties and broad application prospects. It is necessary to estimate accurately the elastic modulus of unidirectional over-braided multilayer composites. In this study, the representative unit cell geometry model of unidirectional over-braided multilayer composites was established. As the braid angle increased from the first to the last layer, two model analytical methods were proposed to predict the elastic modulus of unidirectional over-braided multilayer composites. The prediction results of the two methods had good correlation with the experimental results. The smaller the increment of the braid angle from the first to the last layer, the smaller the difference between the results of the two methods. As a result of the increase in undulation amplitude, the longitudinal modulus of two-dimensional over-braided multilayer composites showed a decrease (7.94%) in comparison to the unidirectional over-braided multilayer composites. In over-braided multilayer composites, the outer layer compacted the inner layer due to the braid tension. In unidirectional over-braided multilayer composites, the interaction between layers could be ignored. In two-dimensional over-braided multilayer composites, the inner layer was obviously compacted by the outer layer. However, as the amplitude and length of the undulation repeat unit of the braided yarn were not affected by the compaction, the reduction in the longitudinal modulus of two-dimensional over-braided multilayer composites caused by compaction was very slight.